Method of making expanded polystyrene partition structure

ABSTRACT

A partition structure for shipping or storage containers having a plurality of interfitting partition strips with interlocking slots and with the partition strips being formed of expanded polystyrene. In one form thereof, the planar faces of a partition strip have a relatively low density because of said surfaces being formed by saw cut from a block of expanded polystyrene, while the entire peripheral edge of the partition strip, including the interlocking slots, are formed by hot wire cutting to have a higher density on the surface thereof to provide greater physical strength for the partition strip.

United States Patent H9} Kuchuris et al.

[ METHOD OF MAKING EXPANDED POLYSTYRENE PARTITION STRUCTURE [75]Inventors: Louis C. Kuchuris, Chicago; Stanley Gembicki, Des Plaines.both of Ill (73] Assignee: Cutting Equipment Leasing, Inc.,

Chicago, Ill.

[22] Filed: Feb. 6, I974 [2| Applt No.: 440,256

Related U.S. Application Data [62] Division of Ser No. 254,749, May 18.I972, Pat. No,

[ 1 Aug. 26, 1975 OTHER PUBLICATIONS Cutting and Fabrication," TechnicalManual Dylite Expandable Polystyrene. Bulletin C9273 Chapter 3h,December I, 1962.

Primary ExumincrRoy Lake Assistant Examinerlames F. Coan Attorney,Agent. or FirmWegner, Stellman, McCord Wiles & Wood [57] ABSTRACT Apartition structure for shipping or storage containers having aplurality of interfitting partition strips with interlocking slots andwith the partition strips being formed of expanded polystyrene. In oneform thereof. the planar faces of a partition strip have a rel ativelylow density because of said surfaces being formed by saw cut from ablock of expanded polystyrene, while the entire peripheral edge of thepartition strip. including the interlocking slots. are formed by hotwire cutting to have a higher density on the surface thereof to providegreater physical strength for the partition strip.

5 Claims. 5 Drawing Figures METHOD OF MAKING EXPANDED POLYSTYRENEPARTITION STRUCTURE This is a division, of application Ser. No. 254,749tiled May I8, 1972 now US. letters Pat. No. 3.837.560.

BACKGROUND OF THE INVENTION This invention pertains to partitionstructure and. more particularly, to partition strips formed of expandedpolystyrene.

Partition structures for shipping and storage containers, as generallyknown prior to this invention, are formed from corrugated papermaterial. Such structures are relatively expensive considering the costof raw materials and labor in manufacture. Apart from the cost thereof,a less than satisfactory partition structure results because the papermaterial has many properties which are undesirable in the shipping andstoring of material. The paper is subject to mold, staining, combustion,water damage and, once subject to crushing forces. does not have anymemory to return to its origi nal shape.

SUMMARY With the partition structure and partition strips disclosedherein and formed of expanded polystyrene, the partition is a relativelyinert structure which is not subject to water damage, mold, staining andis practically noncombustible and a vapor barrier. Additionally, thecost of the raw material and labor, in forming the partition strips, isless than that of conventional corrugated paper partition structure,adding to the advantages thereof. The resulting partition structure isrelatively lightweight and provides the desired cushioning contact andstructural strength for a shipping container without substantialaddition to the shipping weight of the container.

In addition to the novelty of the partition strip formed of expandedpolystyrene, it is possible to provide a one-piece laminate, in effect,with the planar faces of the partition strip being formed by sawcuttingof the strip from a block of expanded polystyrene to have the faces withthe same low density as that of the basic block from which they areformed, while the entire peripheral edge, including the interlockingslots formed in a partition strip, are subject to hot wire formation toprovide melting of the surface of the partition strip along the entireedge. This melting provides a relatively high density layer along thesurface of the partition strip edge to provide added structuralstrengthand also forms a tension surface to provide a prestressed beam effectfor the partition strip. The hot wire forming of the interlocking slots,due to the melt ing of the surface polystyrene, also provides strengthto the interlocking slots.

Additionally disclosed herein is a novel method of forming the partitionstrips wherein a block of expanded polystyrene has its top, bottom andsides and a plurality of interlocking slots shaped by hot wire cuttingto form the higher density surface layer followed by saw cuts ofsuccessive partition strips along a line transverse to the length of theblock to have the exposed planar faces of the partition strip ofunmodified low density expanded polystyrene for cushioning contact witha product.

In view of the foregoing, a general object of this invention is toprovide a new and improved partition structure wherein interlockingpartition strips are formed of expanded polystyrene.

Another object of the invention is to provide a partition strip forinterlocking relation with other such strips to form a partitionstructure usable in shipping or storage containers comprising agenerally planar integral body of expanded polystyrene with the planarfaces of said body having relatively low density for cushioning contactwith the product and the edge of the strip having a higher density foradding structural strength to the strip.

Still another object of the invention is to provide a partitionstructure for shipping and storage containers having a plurality ofinterfitting partition strips with interlocking slots wherein thepartition strips are formed of a molded plastic material and with thepartition strip having generally planar faces with relatively lowdensity for cushioning contact with the product and the peripheral edgeof the strip having a higher density for added structural strength.

A further object of the invention is to provide a method of forming apartition strip and a partition strip resulting from said method whereinsuccessive partition strips are sawed from a block of expandedpolystyrene to have the planar faces thereof of the same density as thebasic block of material and with the slots formed in the partition stripand the entire edge of the strip being preformed prior to sawing by hotwire cutting applied to the block with resulting melting of expandedpolystyrene at the surfaces contacted by the hot wire to form a higherdensity surface layer in the partition strip.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of a toolusable in forming the interlocking slots in a block of expandedpolystyrene prior to formation of an individual partition strip;

FIG. 2 is a perspective view showing the saw'cutting of a partitionstrip from a block of expanded polystyrene;

FIG. 3 is a perspective view of a formed partition strip;

. FIG..4 is a perspective view of a partition structure showing aplurality of interlocked partition strips; and

FIG. 5 is a fragmentary, enlarged view of a part of a partition stripshowing the different density between the major part of the body of thepartition strip and the edge thereof, with the latter being formed byhot wire cutting.

DESCRIPTION OF THE PREFERRED METHOD AND EMBODIMENT In describing themethod, reference may be made to FIGS. 1 and 2 wherein a block I0 ofexpanded polysty rene is shown. This block has a length extending fromleft to right as viewed in FIGS. 1 and 2, with a top II and a bottom(not shown) and with a front side 12 and a rear side (not shown). Oneend is indicated at 15. This block 10 has a height and width equal tothe height and length, respectively, of a partition strip indicatedgenerally at 20 in FIG. 3.

The top 11, bottom and front side 12 and rear side of the block I0 areformed by hot wire cutting prior to the step of the method illustratedin FIG. I. As shown in FIG. I, a tool, which is illustrative only, isprovided for hot wire forming of a plurality of slots 21, 22, and

23 in the partition strip 20. A plurality of hot wires 24, 25 and 26are, as known in the art, electrically heated and suitably mounted in avertically-movable frame, indicated generally at 30, whereby they may belowered into the block 10 to a desired depth to form the interlockingslots 21-23 by melting of the expanded polystyrene. Following formationof the interlocking slots along the entire length of the block 10, theblock 10 is then moved relative to a saw-cut device, such as a band saw,indicated generally at 40, having a travelling blade 41, to cutsuccessive partition strips 20 of the desired thickness from the block10. This is accomplished by relative movement between the block and theblade along a line transverse to the length of the block, withsuccessive repositioning of the block and blade relative to each otherfor a succeeding cut. After the step performed as shown in FIG. 2, thepartition strip 20 is then complete and is as shown in FIG. 3. A seriesof partition strips 200 are then positioned in spaced, parallel relationwith their interlocking slots faced upwardly and are interfitted with aninverted series of parallel spaced partition strips 20b to form thepartition structure illustrated in FIG. 4.

With the method as described herein, the entire peripheral edge of thepartition strip 20 including a bottom edge 50, the front and rear edges51 and 52, respectively, and the top edge 53 including the entiresurface of the interlocking slots 21-23 are initially formed by hot wirecutting which results in melting of the expanded polystyrene. Thismelting results in a relatively high density surface layer, asillustrated at 60 in FIG. 5, while the major part of the partition stripis of a low density and the same as that of the basic block 10 ofexpanded polystyrene and as indicated at 6| in FIG. 5. This results inthe formation of a tension surface for the partition strip about theentire edge thereof having a higher density for structural strength and,in effect, providing a prestressed beam effect for the partition strip,and with resultant strengthening of the bottom of the interlockingslots.

The generally planar partition strip 20 has a pair of opposed planarfaces, with one face 70 shown in FIG. 3 and with each of these facesbeing formed by the sawcut step of the method illustrated in FIG. 2. Thesaw cut results in the formation of the partition strip from the blockwithout creating any dust and without any modification of the density ofthe planar surface whereby the density is the same as that of the basicblock and is of a relatively low value. This results in soft" surfacesfor the partition strips which can be in cushioning contact with aproduct in a shipping or storage container and when the partition stripsare assembled into the partition grid structure illustrated in FIG. 4.

The partition strips of expanded polystyrene are capable of meeting manydifferent packaging requirements. The basic block can be selected tohave a density in the range of 1 pound per cubic foot, or less, up to adensity of 4 to 5 pounds per cubic foot. This results in planar facesfor the partition strip which are relatively soft but which still have amemory to return to the initial shape after compression The surfacelayer density along the peripheral edge of the partition strip and inthe slots 21-23 of the strip can then be controlled by the hot wirecutting process, with density variation being controlled by thetemperature of the wire, the diameter of the wire. and the speed oftravel of the wire relative to the block 10 in the formation of theslots as well as the initial shaping of the block 10. Additionally, thesize of the slots 21-23 of the partition strip 20 can also be varied bycontrol of the temperature, diameter, and speed of travel of the wires2426, shown in FIG. I.

With the structure and process disclosed herein, it will be seen thatpartition strips are provided of relatively low-cost basic material andminimal production cost wherein the partition strip, in effect, is anintegral laminate with a high density peripheral edge surface to providefor handling strength and resistance to crushing of the partition strip,while the planar faces thereof are of low density to provide maximumcushioning effeet in contact with products.

Examination of a partition strip made by the process disclosed hereinshows that the planar faces thereof have a relatively smooth, softsurface, while the peripheral edge around the entire partition strip,including the interlocking slots, has a rougher and harder surface.

As an example, partition strips of expanded polystyrene have been foundto perform satisfactorily wherein the density of the basic block 10 isapproximately onehalf pound per cubic foot and with the peripheral edgeof the strip being formed by hot wire cutting to have a surface layerwith a density of approximately 4t) pounds per cubic foot. These valuesare not limiting, but are only given as an example of one particularstrip made by the process disclosed herein.

We claim:

I. A method of forming a partition strip of expanded polystyrenecomprising the steps of: shaping a block of polystyrene to a width andheight equal to the desired length and height ofa partition strip by hotwire cutting along the top, bottom and sides of the block; forming aseries of spaced slots extending lengthwise of the block by hot wireforming to a depth sufficient to provide for subsequent interlockingwith other strips; and sawing said block along a line transverse to thelength thereof in successive cuts to form individual partition stripswith relative soft planar faces for contact with a product while theentire exposed edge of the strip including said slots and the bottomthereof has a higher surface density resulting from the hot wire cuttingto provide added physical strength to the partition strip.

2. A method of forming a partition strip of expanded polystyrenecomprising the steps of: forming a series of spaced slots by hot wirecutting in a block of expanded polystyrene to a depth sufficient toprovide interlocking slots for assembly with other partition strips,sawing a partition strip from said block, and subjecting the entireedges of said partition strip to a hot wire to form a higher densitysurface along said edges.

3. The method of claim 2 in which the step of subjecting the entireedges of said partition strip to a hot wire to form a higher densitysurface along said edges includcs the step of shaping the block to awidth and height equal to the desired length and height of the partitionstrip by hot wire cutting along the top, bottom and sides of the block.

4. The method of claim 2 in which the step of sawing a partition stripfrom said block is successively repeated to form a plurality ofpartition strips, and said edges of the partition strip are subjected toa hot wire prior to sawing the strip from the block.

5. The method of claim 2 in which the hot wire cutting results in adensity increase in the polystyrene adjathe wire at a selectedtemperature and moving the wire into the block at u selected speedcorresponding to the desired density.

1. A METHOD OF FORMING A PARTITION STRIP OF EXPANDED POLYSTYRENECOMPRISING THE STEPS OF: SHAPING A BLOCK OF POLYSTYRENE TO A WIDTH ANDHEIGHT EQUAL TO THE DESIRED LENGTH AND HEIGHT OF A PARTITION STRIP BYHOT WIRE CUTTING ALONG THE TOP, BOTTOM AND SIDES OF THE BLOCK, FORMING ASERIES OF SPACED SLOTS EXTENDING LENGTHWISE OF THE BLOCK BY HOT WIREFORMING TO A DEPTH SUFFICIENT TO PROVIDE FOR SUBSEQUENT INTERLOCKINGWITH OTHER STRIPS, AND SAWING SAID BLOCK ALONG A LINE TRANSVERSE TO THELENGTH THEREOF IN SUCCESSIVE CUTS TO FORM INDIVIDUAL PARTITION STRIPSWITH RELATIVE SOFT PLANAR FACES FOR CONTACT WITH A PRODUCT WHILE THEENTIRE EXPOSED EDGE OF THE STRIP INCLUDING SAID SLOTS AND THE BOTTOMTHEREOF HAS A HIGHER SURFACE DENSITY RESULTING FROM THE HOT WIRE CUTTINGTO PROVIDE ADDED PHYSICAL STRENGTH TO HE PARTITION STRIP.
 2. A method offorming a partition strip of expanded polystyrene comprising the stepsof: forming a series of spaced slots by hot wire cutting in a block ofexpanded polystyrene to a depth sufficient to provide interlocking slotsfor assembly with other partition strips, sawing a partition strip fromsaid block, and subjecting the entire edges of said partition strip to ahot wire to form a higher density surface along said edges.
 3. Themethod of claim 2 in which the step of subjecting the entire edges ofsaid partition strip to a hot wire to form a higher density surfacealong said edges includes the step of shaping the block to a width andheight equal to the desired length and height of the partition strip byhot wire cutting along the top, bottom and sides of the block.
 4. Themethod of claim 2 in which the step of sawing a partition strip fromsaid block is successively repeated to form a plurality of partitionstrips, and said edges of the partition strip are subjected to a hotwire prior to sawing the strip from the block.
 5. The method of claim 2in which the hot wire cutting results in a density increase in thepolystyrene adjacent the cut, and the precise change in density varieswith the temperature of the wire, the diameter of the wire, and thespeed of travel of the wire relative to the block, and said step offorming a series of spaced slots by hot wire cutting includes the stepsof maintaining the wire at a selected temperature and moving the wireinto the block at a selected speed corresponding to the desired density.